A squealing ATV belt is a sign that something is not quite right with either the clutch assembly or the belt itself. It’s an annoying issue that may or may not be hard to fix at home.

To make the troubleshooting a bit easier, we have structured the post according to the various symptoms your ATV may be having. Under each symptom, we address the different issues that may be causing the behavior you are experiencing.

Caution! Never turn on the key, start the engine, or run a four-wheeler with the clutch cover off. It is not only potentially very dangerous; it may mess up components such as the KEBC actuator memory (Kawasaki ATVs).

Symptom: The belt squeals at idle but the noise goes away when applying throttle

This is the most typical behavior when struggling with ATV belt squeal. This symptom has a range of possible causes.

With the bike in gear and at idle, the primary clutch should usually be spinning freely without the clutch sheaves touching the belt. As you apply throttle, the gap between the clutch sheaves gradually tightens so that it grabs and starts spinning the belt.

When the clutch sheaves for some reason is grabbing the belt slightly when it should not, you get belt squeal. It’s the friction between rubber and metal is that is causing the characteristic squealing sound.

Along with the squealing sound at idle, the bike may be having the following symptoms:

The ATV is hard to shift in and out of gear

When the clutch sheaves are not spinning freely at idle, it causes tension on the gears inside the transmission. The tension between the gears may require that you use excessive force to operate the gear shifter. In some cases, you won’t be able to shift gears at all.

The squealing sound stops when shifting to neutral

When in neutral, the primary clutch should not be spinning and is therefore not able to afflict any force to the belt.

The squealing sound typically begins when the bike shifts into gear and the primary clutch activates.

Possible cause 1: The belt is too wide

Belt size tolerances on a CVT transmission are small. A belt that is just a fraction too wide may cause unwanted rubbing issues.

How to fix it

Use an OEM belt

Aftermarket belts can offer better value, better performance, or both. But they may also be the cause of your belt squeal issues.

The reason can be small variations in manufacturing tolerances.

Most of the time, an aftermarket belt will work just fine. But when faced with a mysterious belt squealing issue, where no cause is to be found, your best bet is to install an OEM belt to see if this helps.

On the numerous ATV forums, you will find the same story over and over. After several failed attempts, the noise disappeared entirely after installing an original belt.

As most instances of belt squeal are belt-related in some way or form, we recommend that you always try with an OEM belt before spending time and money on the clutches themselves.

Let the belt break-in properly

A new belt will need a few miles of running time to break-in. Allow the specified break-in period to finish as this may be all that it takes to remove the belt noise.

When the belt wears, some people remove one or more clutch shims. This will decrease the width between the sheaves slightly, compenating for belt wear. Maybe it was yourself who did this some time ago, or a previous owner may have done it.

When installing a new belt, it is going to be slightly wider than the old worn one. Even with just one shim short from stock, you may get rubbing, causing belt squeal at idle.

How to fix it

You can adjust the distance between the sheaves of the primary clutch at idle is by adding or removing shims. This allows for fine adjustment according to belt width.

The job can be done at home if you have the tools required to split the clutch. If you don’t, your best option is removing the complete clutch assembly and taking it to a dealer to do the shimming for you.

This video demonstrates shimming a snowmobile primary clutch. The same basic principles applies to an ATV clutch.

Possible cause 3: The belt is installed in the wrong direction

The proper way of installing a CVT belt is so that you can read the part number when standing next to the ATV.

If it reads up-side-down, the belt is mounted the wrong way. This can, in some cases, cause belt squeal.

How to fix it

At idle, the belt should not be touching the sheaves of the primary clutch, but resting against a bearing outside the clutch shaft.

If this bearing starts to wear or jams up completely, it won’t spin as it should. Instead, it will start rubbing against the inside of the belt.

How to fix it

With the engine off, remove the clutch cover.

Remove the drive belt and locate the center bearing. It should look almost like a serpentine pulley on a car.

Grab the center bearing with two fingers and try to turn it. It should spin freely. If you feel any dragging, grinding, or that it is stuck, you need to address this issue.

A bearing that is contaminated with sand, for example, from submerging the ATV, can often be salvaged. Ideally, it should be taken apart for a thorough cleanse and lube, but this requires special tools.

As it is essential to remove any moisture before the bearing starts to rust, you can try cleaning the bearing without removing it.

Use an air compressor to blow it as clean as you can.

Then spray it with WD-40 while trying to spin the sleeve with a pair of vice grips. Note that ATVs that have EBS systems use a one-way bearing. Do not try forcing the bearing to rotate in the locked direction.

If the bearing had time to rust, it likely needs replacing.

If the bearing is worn, it needs replacing as well. The job is relatively quick but requires special tools. If you don’t have these tools available, it will be easiest to pull off the complete clutch and bring it to the dealer to have the bearing replaced. This repair will typically cost $100 to $150.

Possible cause 5: The clutches need a cleanse

All of the components inside the clutches need to be moving freely for the clutches to be working correctly. Dirt and dust from worn components may lock up the rollers and other moving parts so that the clutch does not engage or disengage completely.

How to fix it (fast cleanse)

With the engine off, remove the clutch cover.

Put on a dust mask; you do not want to breathe the fine dust trapped inside the clutches.

Use an air compressor to blow the clutches as clean as possible.

Reinstall the clutch cover and see if this helped. If not, you may need to disassemble the clutch assembly for a more thorough clean.

Possible cause 6: Worn clutch components

Worn components may also prevent the sheaves from moving as they should. Typical parts to address are:

Worn rollers.

Worn Teflon bushings. Look for metallic looking or shiny dust, as this may be a sign of worn bushings.

Worn or damaged helix (less common)

Service the clutch by replacing worn parts. You can do this yourself or take it to a dealer if you don’t have the tools needed to disassemble a clutch safely.

This post does not cover how to disassemble a clutch; the steps vary depending on what brand and model of ATV you have.

Possible cause 7: Worn or broken motor mounts

If the motor mounts are worn or broken, you may find that the clutches are out of alignment.

How to fix it

Inspect your motor mounts. Replace any worn or damaged motor mounts.

Possible cause 8: Belt deflection is set too tight (common issue)

Too little deflection means that the belt is too tight. When the belt is too tight, it may be engaging slightly at idle, when it should be spinning freely. Symptoms such as reduced top RPM is a sign of too-tight belt deflection.

Continue reading below to learn how you can adjust belt deflection whether it is too toght or too loose.

Symptom: The belt squeals just as the ATV starts moving

In some cases, there is no squealing when the bike is cold, but as soon as the belt heats up, you start getting squealing sounds when you take off.

Possible cause: Belt deflection is too loose

Belt deflection is the distance the belt deflects from its neutral position when pushing down on it, right between the two clutches.

Excessive deflection means that the belt is too loose. When belt deflection is too loose, the belt will fall down into the secondary clutch, while it climbs in the primary. This is comparable to starting a car in 4th gear instead of first. Typical symptoms are bogging down the engine at take-off.

How to fix it

Measure the belt deflection

Some service manuals will tell you to measure belt deflection by applying pressure to the belt by hand. While this is ok for most home mechanics, it may not be accurate enough to address the most stubborn cases of belt squeal.

A more precise method is applying a specified level of down pressure, using a scale.

How to measure belt squeal by hand (good accuracy):

With the engine off, remove the clutch cover.

Place a flat object like a ruler between the primary and the secondary clutch.

Press down on the belt in the middle of the clutches with one finger. Do not push too hard as it will just cause the sheaves to slide apart. According to the user manual, you should “push down on the drive belt until it is lightly tensioned.”

Measure the belt deflection as the distance between the ruler and the belt. Your owner’s manual should tell you the correct belt deflection on your bike. The belt deflection should typically be in the range of ⅞” to 1 ¼”.

How to measure belt deflection using a scale (better accuracy):

Step one and two and four are identical to the above method.

But when applying pressure on the belt, instead of estimating the force to apply, you are using a scale.

Your service manual will tell you the correct pressure to apply to get an accurate reading. If you don’t have one, 13lb (6kg) of force is a good rule of thumb.

You don’t need a specialist tool to do this at home. With a zip tie and a cheap fish scale, you will get decent accuracy.

My scale does not go high enough, and I’m not able to hold a ruler while I’m taking the photo, but you get the idea. Measure how much the belt deflects from normal when pulling the scale at the specified rate.

Adjust the belt deflection if necessary

Belt deflection is typically adjusted by turning an adjustment screw on the secondary clutch, or by adding or removing spacer shims in the secondary clutch.

Adjusting belt deflection on an ATV secondary clutch that has an adjustment screw:

Loosen the locking nut that holds the adjustment screw in place.

Turn the adjustment screw either clockwise or counterclockwise.

Turning the screw counterclockwise will bring the sheaves together, tightening the belt.

Turning the screw clockwise will bring the sheaves further apart, making the belt loose.

Grab the belt and roll it through the primary and the secondary after adjusting. This will ensure that the belt falls in place between each adjustment.

Measure deflection and adjust accordingly until the deflection is according to spec.

Adjusting belt deflection on an ATV secondary clutch that uses shims:

As with the primary, the shimming of a secondary clutch can be done at home if you have the right tools. Again, if you don’t have the tools or skills, your best option is removing the complete clutch assembly and taking it to a dealer to do the shimming for you. Alternatively, you can bring the whole ATV.

Symptom: The ATV squeal when moving

Some noise and vibration when driving are normal on any CVT clutch.

Installing a snorkel may enhance these sounds. As so will pulling heavy loads at low speeds.

But sometimes, the noise is above what is normal.

Possible cause 1: The sheaves are dirty

Clutch sheaves may get dirty from a spinning ATV belt or from not cleaning a new belt with soap and hot water before installing it as you should.

How to fix it

With the engine off, remove the clutch cover and drive belt.

Use a Scotch Brite pad and some hot soapy water to clean off any residue. Using sandpaper is not recommended as this may cause increased belt wear and reduce its service life.

Blow everything clean with compressed air before reinstalling the belt and clutch cover.

Possible cause 2: Running higher rate clutch springs

Running bigger tires cause excess stress on the drive belt. If you go up more than one inch in size, you need stiffer clutch springs to accommodate the added stress.

Stiffer springs cause more belt noise due to the added tension. It is normal to hear a noticeable difference between your stock setup.

Welcome to Boost ATV

Hi, I’m Haavard, and I’m the guy behind Boost ATV. I grew up on a farm where ATVs have been and still are an important part of “getting things done”. I also enjoy the thrill and joy of the occasional trail ride. So I made this site to write about the things I have learned. Hopefully, you will find it useful!

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